The present invention relates to a simple thermostat in a package having two terminals for mounting to a printed circuit board.
A DIP (dual in-line package) is an electronic component available in several standard sizes and includes a housing having downward extending terminal pins which are received in plated through holes of a PCB. The chip or the like in the housing is thus connected to circuitry and other components.
U.S. Pat. No. 4,620,175, which is incorporated herein by reference, discloses a simple thermostat configured as a standard DIP having four terminal pins. Since the package is virtually identical to a standard DIP, it does not require any special hole spacing by the PCB manufacturers or any special assembly equimment. The terminal pins come in two pairs, the pins in each pair being connected through a single inward end inside the housing so as to be electrically redundant.
The housing includes a floor, opposed parallel sidewalls, and opposed parallel endwalls which define a cavity therebetween. The housing is molded onto first and second terminals so that the inward ends are exposed at opposite ends of the floor and the pins extend downward therefrom through the housing. A contact arm is fixed to the inward end of the first terminal and has a cantilever arm whose free end has a contact fixed thereto and is biased away from but movable toward a fixed contact on the inward end of the second terminal. A fulcrum plate having a central dimple is fixed between the sidewalls and a bimetal strip is located between the fulcrum plate and the contact arm. The bimetal strip has two stable positions (bistable); in a first stable position the strip is bowed convexly against the dimple and biases the contact on the contact arm against the contact on the second terminal to complete the circuit between the first and second terminals. In the second stable position, which occurs above a predetermined temperature, the bimetal strip is bowed concavely toward the dimple so that the contact arm springs away from the second terminal to open the circuit. The foregoing describes an "open on rise" thermostat; a "close on rise" device can be provided simply by inverting the bimetal strip.
The DIP thermostat is intended for mounting in airflow sufficient to activate the switch conduction from the ambient air. It would also be desirable to provide a board mounted thermostat suitable for sensing the surface temperature of a heat sink or cabinet.